Image sensors such as complementary metal-oxide semiconductor (CMOS) image sensors (CIS) are used for sensing an imcoming radiation projected towards a semiconductor substrate and widely used in various applications such as video camera, digital still camera and the like. These devices utilize an array of pixels or image sensor elements, to collect photo energy to convert images into electrical signals.
A pixel of CMOS image sensor includes a photo detector such as a photodiode, photogate detector, or phototransistor. However, defects may occur during fabricating the CMOS image sensors, thereby generating noises of pixels. Accordingly, a CMOS image sensor has to be continuously improved so as to obtain a more satisfactory device.